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.TH FREOPEN 3C "March 25, 2020"
.SH NAME
freopen \- open a stream
.SH SYNOPSIS
.nf
#include <stdio.h>

\fBFILE *\fR\fBfreopen\fR(\fBconst char *\fR\fIfilename\fR, \fBconst char *\fR\fImode\fR, \fBFILE *\fR\fIstream\fR);
.fi

.SH DESCRIPTION
The \fBfreopen()\fR function first attempts to flush the stream and close any
file descriptor associated with \fIstream\fR. Failure to flush or close the
file successfully is ignored. The error and end-of-file indicators for the
stream are cleared.
.sp
.LP
The \fBfreopen()\fR function opens the file whose pathname is the string
pointed to by \fIfilename\fR and associates the stream pointed to by
\fIstream\fR with it. The \fImode\fR argument is used just as in
\fBfopen\fR(3C).
.sp
.LP
If \fIfilename\fR is a null pointer and the application conforms to SUSv3 (see
\fBstandards\fR(7)), the \fBfreopen()\fR function attempts to change the mode
of the stream to that specified by \fImode\fR, as though the name of the file
currently associated with the \fIstream\fR had been used. This behavior
is not supported by streams that are backed by memory, such as
\fRfmemopen\fB(3C). The following changes of mode are permitted, depending upon
the access mode of the file descriptor underlying the stream:
.RS +4
.TP
.ie t \(bu
.el o
When \fB+\fR is specified, the file descriptor mode must be \fBO_RDWR\fR.
.RE
.RS +4
.TP
.ie t \(bu
.el o
When \fBr\fR is specified, the file descriptor mode must be \fBO_RDONLY\fR or
\fBO_RDWR\fR.
.RE
.RS +4
.TP
.ie t \(bu
.el o
When \fBa\fR or \fBw\fR is specified, the file descriptor mode must be
\fBO_WRONLY\fR or \fBO_RDWR\fR.
.RE
.sp
.LP
If the filename is a null pointer and the application does not conform to
SUSv3, \fBfreopen()\fR returns a null pointer.
.sp
.LP
The original stream is closed regardless of whether the subsequent open
succeeds.
.sp
.LP
After a successful call to the \fBfreopen()\fR function, the orientation of the
stream is cleared, the encoding rule is cleared, and the associated
\fBmbstate_t\fR object is set to describe an initial conversion state.
.sp
.LP
The largest value that can be represented correctly in an object of type
\fBoff_t\fR will be established as the offset maximum in the open file
description.
.SH RETURN VALUES
Upon successful completion, \fBfreopen()\fR returns the value of \fIstream\fR.
Otherwise, a null pointer is returned and \fBerrno\fR is set to indicate the
error.
.SH ERRORS
The \fBfreopen()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEACCES\fR\fR
.ad
.RS 16n
Search permission is denied on a component of the path prefix, or the file
exists and the permissions specified by \fImode\fR are denied, or the file does
not exist and write permission is denied for the parent directory of the file
to be created.
.RE

.sp
.ne 2
.na
\fB\fBEBADF\fR\fR
.ad
.RS 16n
The application conforms to SUSv3, the \fIfilename\fR argument is a null
pointer, and either the underlying file descriptor is not valid or the mode
specified when the underlying file descriptor was opened does not support the
file access modes requested by the \fImode\fR argument.
.RE

.sp
.ne 2
.na
\fB\fBEFAULT\fR\fR
.ad
.RS 16n
The application does not conform to SUSv3 and the \fIfilename\fR argument is a
null pointer.
.RE

.sp
.ne 2
.na
\fB\fBEINTR\fR\fR
.ad
.RS 16n
A signal was caught during \fBfreopen()\fR.
.RE

.sp
.ne 2
.na
\fB\fBEISDIR\fR\fR
.ad
.RS 16n
The named file is a directory and \fImode\fR requires write access.
.RE

.sp
.ne 2
.na
\fB\fBELOOP\fR\fR
.ad
.RS 16n
Too many symbolic links were encountered in resolving \fIpath\fR.
.RE

.sp
.ne 2
.na
\fB\fBEMFILE\fR\fR
.ad
.RS 16n
There are {\fBOPEN_MAX\fR} file descriptors currently open in the calling
process.
.RE

.sp
.ne 2
.na
\fB\fBENAMETOOLONG\fR\fR
.ad
.RS 16n
The length of the \fIfilename\fR exceeds {\fIPATH_MAX\fR} or a pathname
component is longer than {\fINAME_MAX\fR}.
.RE

.sp
.ne 2
.na
\fB\fBENFILE\fR\fR
.ad
.RS 16n
The maximum allowable number of files is currently open in the system.
.RE

.sp
.ne 2
.na
\fB\fBENOENT\fR\fR
.ad
.RS 16n
A component of \fIfilename\fR does not name an existing file or \fIfilename\fR
is an empty string.
.RE

.sp
.ne 2
.na
\fB\fBENOSPC\fR\fR
.ad
.RS 16n
The directory or file system that would contain the new file cannot be
expanded, the file does not exist, and it was to be created.
.RE

.sp
.ne 2
.na
\fB\fBENOTDIR\fR\fR
.ad
.RS 16n
A component of the path prefix is not a directory.
.RE

.sp
.ne 2
.na
\fB\fBENXIO\fR\fR
.ad
.RS 16n
The named file is a character special or block special file, and the device
associated with this special file does not exist.
.RE

.sp
.ne 2
.na
\fB\fBEOVERFLOW\fR\fR
.ad
.RS 16n
The current value of the file position cannot be represented correctly in an
object of type \fBoff_t\fR.
.RE

.sp
.ne 2
.na
\fB\fBEROFS\fR\fR
.ad
.RS 16n
The named file resides on a read-only file system and \fImode\fR requires write
access.
.RE

.sp
.LP
The \fBfreopen()\fR function may fail if:
.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 16n
The value of the \fImode\fR argument is not valid.
.RE

.sp
.ne 2
.na
\fB\fBENAMETOOLONG\fR\fR
.ad
.RS 16n
Pathname resolution of a symbolic link produced an intermediate result whose
length exceeds {\fIPATH_MAX\fR}.
.RE

.sp
.ne 2
.na
\fB\fBENOMEM\fR\fR
.ad
.RS 16n
Insufficient storage space is available.
.RE

.sp
.ne 2
.na
\fB\fBENXIO\fR\fR
.ad
.RS 16n
A request was made of a non-existent device, or the request was outside the
capabilities of the device.
.RE

.sp
.ne 2
.na
\fB\fBETXTBSY\fR\fR
.ad
.RS 16n
The file is a pure procedure (shared text) file that is being executed and
\fImode\fR requires write access.
.RE

.SH USAGE
The \fBfreopen()\fR function is typically used to attach the preopened
\fIstreams\fR associated with \fBstdin\fR, \fBstdout\fR and \fBstderr\fR to
other files. By default \fBstderr\fR is unbuffered, but the use of
\fBfreopen()\fR will cause it to become buffered or line-buffered.
.sp
.LP
The \fBfreopen()\fR function has a transitional interface for 64-bit file
offsets.  See \fBlf64\fR(7).
.SH ATTRIBUTES
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
_
MT-Level	MT-Safe
.TE

.SH SEE ALSO
.BR fclose (3C),
.BR fdopen (3C),
.BR fopen (3C),
.BR stdio (3C),
.BR attributes (7),
.BR lf64 (7),
.BR standards (7)
